Proton Bragg-peak therapy has been utilized for pituitary ablation but rarely to treat disease in other organs, due to the inability to locate accurately the beam terminus which may be irregularly displaced by variations in tissue density. Pilot studies satisfactorily located the end of the proton beam in lucite using NaI detectors; the coincidence counts of the positron annihilation gammas from oxygen 15 activated by the protons were measured. Extrapolation of these results to a clinical situation indicates that the end of the beam range can be defined. Control of the range by a shaped bolus was documented. The research goals are 1) to assemble and adapt a positron camera on-line to locate the end of range of a 200 MeV proton beam in phantoms and animals using O15 activated by the beam, and 2) to construct rapidly a bolus that will limit the range of protons to a selected boundary after passing through heterogeneous tissues. The plan includes cooperative development of a biomedical proton facility equipped for positron imaging, computerized data analysis and display, reproducible target positioning, and efficient bolus construction. When the method and instruments are successfully developed, treatment plans for radiotherapy of selected tumor-containing volumes in the thorax and abdomen will be tested on swine and evaluated.